The present invention relates generally to gas turbine engines, and, more specifically, to turbine blade cooling.
In a gas turbine engine air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream to a turbine which extracts energy therefrom. A high pressure turbine (HPT) first receives the hottest combustion gases for extracting energy therefrom to power the compressor. And, a low pressure turbine (LPT) follows the HPT for extracting additional energy from the combustion gases for providing output power which may be used to drive a fan disposed upstream of the compressor in a turbofan engine for powering an aircraft in flight.
The HPT includes a row of hollow turbine blades extending radially outwardly from the rim of a supporting turbine disk, with each blade having a suitable internal cooling circuit therein in which compressor air is channeled for cooling the blade being heated by the hot combustion gases during operation. The blade requires suitable cooling for maintaining the structural integrity thereof and ensuring a suitable useful life during operation.
However, the air used for cooling the turbine blades is extracted from the compressor and is therefore not used in the combustion process, and correspondingly decreases overall efficiency of the gas turbine engine. Accordingly, it is desired to reduce the amount of cooling air for maintaining engine efficiency, yet sufficient airflow must be provided for adequately cooling the blades.
The amount of required cooling air is referred to as chargeable airflow and is a primary design objective which should be minimized. However, the chargeable flow is controlled by pressure losses, air leakage, and relative temperature increase as the pressurized air is channeled from the compressor to the turbine.
The resulting turbine cooling air delivery system or circuit includes stationary or stator components from the discharge end of the compressor axially along the combustor which must cooperate with the rotating turbine disk for channeling the cooling air thereto. The individual turbine blades have bottom air inlets extending through the dovetails thereof, with the dovetails being retained in corresponding dovetail slots in the rim of the turbine disk.
A typical cooling air delivery system includes a stationary inducer for preswirling the compressor air in the direction of rotation of the turbine disk for minimizing pressure losses therebetween. Rotating impeller vanes are often located near the turbine disk for pumping the airflow through a dedicated flowpath terminating at the disk rim. And, labyrinth seals are used between the stationary inducer and the rotating disk to minimize undesirable leakage of the cooling air from its flowpath to the disk rim.
A particular dilemma in designing the turbine cooling circuit is that large exit diameter inducers are desired for reducing relative air temperature, yet the correspondingly large diameter seals require larger seal gaps and experience increased cooling air leakage adding to chargeable flow. And, since the teeth of the labyrinth seal rotate during operation, the large diameter thereof in a typical gas turbine engine application is greater than the free hoop diameter for which they would be otherwise self-supporting under their own centrifugal load.
Accordingly, the large diameter seal teeth must be supported on an integral supporting disk for withstanding the centrifugal loads generated during operation, which increases the complexity and weight of the cooling system.
Furthermore, air from the stationary inducer must be transferred to corresponding apertures rotating with the turbine disk during operation. Those rotating apertures are preferably small, have unitary aspect ratios, and large pitch spacing of about two diameters for minimizing stress in a radial hoop member in which they are found while maintaining acceptable strength for rotary operation. However, the small transfer apertures introduce corresponding pressure drops and reduce the desired swirl carryover to the rotating disk.
Accordingly, it is desired to provide a turbine cooling air delivery circuit having reduced chargeable flow while maintaining suitable durability.
A turbine cooling circuit includes a flow sleeve having an aft end for adjoining the rim of a turbine disk. A seal rotor is spaced from the aft end adjacent a row of inlet holes. An inducer has an outlet disposed radially outwardly from the sleeve inlet holes. And, a seal stator surrounds the seal rotor to define a rotary seal disposed radially inwardly from the inducer outlet.